This invention relates to the fitting of needle components to the barrel of a hypodermic syringe.
It is common practice to fit a syringe with a filling needle for the purpose of drawing liquid into the barrel of the syringe by retraction of its plunger from a vial often of the kind having a rubber cap which is penetrated by the filling needle. After the syringe has been charged, the filling needle is removed and replaced by a needle to be used for administration of an injection into a patient. Yet again it is often necessary to change a needle to meet patient requirements.
During the change of needle where the syringe is of a type having a large open end to permit needle retraction, care must be taken to avoid spillage of the contents of the syringe through the open end of the barrel.
It is an object of the present invention to provide a seal for the open end of a syringe barrel which overcomes the problem aforesaid.
According to the present invention there is provided a seal adapted to be fitted over the open end of the barrel of a hypodermic syringe comprising a cap of a non-latex elastomer having a central aperture which is sufficiently small as ordinarily to retain liquid therebehind but which can be deformably expanded to allow passage of a needle mounting portion for engagement with the barrel.
The cap may be of silicone rubber.
The aperture may be circular.
The aperture may take the form of a number of slits extending radially outward from the centre of the cap.
The cap may comprise a circular disc having a cylindrical skirt extending from its rear face.
The internal periphery of the skirt may be provided with axially spaced circumferential ribs adapted to engage with circumferential grooves on the end of the barrel to hold the cap in position.
The invention also includes a syringe barrel fitted with a seal as aforesaid.
The syringe barrel may be used with both a filling needle assembly and an injection needle assembly in which case the cap is expandable to allow fitting of both the filling needle and the injection needle to the barrel.
The arrangement may be such that the mounting portion of the injection needle is engaged with the barrel through a one-way coupling means formed by interfitting components on the needle mounting portion and the barrel whereby the injection needle once assembled to the barrel cannot be disengaged from the barrrel (at least not without damaging the components). The filling needle may also be engageable with the barrel with the aid of the one-way coupling means associated with the barrel but in such a way that the filling needle may be subsequently disengaged.
The one way coupling means may comprise a threaded connection or a bayonent-type connection between a male part and a female part, one part being associated with the barrel and the other part being associated with the barrel.
The one way coupling means may for example comprise a threaded connection between a male and a female part, there being a void in an upstanding portion of the thread on each part and a barb in the void on one of the parts, the arrangement being such that when the parts are threadedly engaged, resilient deformation of at least one of the parts enables the barb to latch behind an end of a thread at the void in the other of the parts to prevent subsequent disconnection of the parts.
Another aspect of the invention concerns a threaded connection between a male part and a female part which, when properly threadedly engaged, cannot be disconnected, particularly, though by no means exclusively, suitable for joining components of fluid handling medical devices such as syringes, cannulas and catheters for example.
According to this aspect of the invention there is provided a threaded connection between a male and a female part, there being a void in an upstanding portion of the thread on each part and a barb in the void on one of the parts, the arrangement being such that when the parts are threadedly engaged, resilient deformation of at least one of the parts enables the barb to latch behind an end of a thread at the void in the other of the parts to prevent subsequent disconnection of the parts.
There may be on each part a two-start thread, the upstanding portion of each thread having a circumferential extent of less than 180xc2x0 whereby there are voids between the ends of the two threads on each part and diametrically opposed barbs in the voids on the male part.
The height of each thread on the female part may increase from one end to the other which provides the abutment against which a barb latches.